1. Field of the Invention
The invention relates to a system for introducing redundant binary data in a plurality of parallel serial streams into a medium, and for extracting those binary data again, where the redundancy allows for correcting certain types of data errors. The medium may be a material that is locally magnetizable, or that may locally be modified by optical, for example laser, means and which is driven along a write/read device.
In this case "introduction" is to be understood to mean "writing" and "extracting" is to be understood to mean "reading". Alternatively a plurality of parallel data communication channels may be present. In that case, "introducing" relates to "transmission" and "extracting" relates to "reception".
2. Description of the Prior Art
A device of the described kind is known from U.S. Pat. No. 3,697,947. The known technique concerns three data channels and one error correction channel and is based on a convolutional code. The generation of the error correction bits is realized by means of EXCLUSIVE-OR logic or modulo-2 addition. An arbitrary error in a group of three parallel data bits can be corrected by the convolutional code used. Obviously, such mutilated three-bit characters must be spaced sufficiently apart. The invention, however, is based on the recognition of the fact that errors in many instances are limited to only a few data channels in each of which a string or errors may occur in quick succession. The known code does not offer a solution in this respect. A system for transmitting binary data via a plurality of channels in which an error string occurring in a single channel at a time would be rendered correctable by the addition of two redundant channels has been described in the U.S. Pat. No. 4,395,768 issued July 26, 1983, now abandoned to Jean M. E. B. Goethals et al and assigned to the assignee of the present application, herein incorporated by reference. However, this earlier application allows for correction of only a single erroneous channel at a time.
Introduction of more redundancy along the concept of the prior invention would not, in many cases, allow for an increased error correction capability.